1. Field of the Invention
The present invention generally relates to a hard drive accessing method and a hard drive accessing system, and more particularly, to a hard drive accessing method and a hard drive accessing system which support a maximum transmission rate of a hard drive.
2. Description of Related Art
Along with the development of electronics technology, different mobile devices, such as cell phones, personal digital assistants (PDAs), and notebook computers, have been developed and brought into the market. This kind of mobile devices has become very popular among consumers due to such characteristics thereof as small volume, light weight, and diversified functionality. If disposed with a high-speed processor and a large-capacity storage medium, such a mobile device can perform various functions such as camera, phone conversation, and Internet access, or even some higher-level functions such as multimedia playing, game, and navigation. In short, a mobile device can provide very convenient and diversified functions to its user.
Power supply is one of the most important issues to a mobile device. In order to reduce the power consumption of a mobile device system, the mobile device is usually switched to a central processing unit (CPU) enhanced power mode when the system thereof enters an idle state. In this CPU enhanced power mode, a phase locked loop (PLL) in the controller is turned off. The controller issues a power management event (PME) message to wake up the CPU when the hard drive issues an interrupt or a direct memory access (DMA) request. However, after the CPU is waken up, signal phase shift between the controller and the hard drive may be caused due to their hardware design, and accordingly the clock signal of the controller cannot be correctly synchronized with the clock signal of the hard drive. As a result, the hard drive can not be accessed correctly. In this case, the transmission rate of the hard drive has to be reduced to stabilize the system.
For example, the existing standard specification of an integrated drive electronics (IDE) hard drive supports 7 ultra direct memory access (UDMA) modes, and each of the UDMA modes is corresponding to a specific transmission rate (as shown in table 1), wherein the transmission rates gradually increase from mode 0 to mode 6, and the transmission rate 133 MB/s corresponding to mode 6 is the highest.
TABLE 1ModeModeModeModeModeModeModeMode0123456Transmission16.725.033.344.466.7100133rate (MB/s)
FIG. 1 is a diagram of a conventional hard drive assessing method. Referring to FIG. 1, assuming the maximum transmission rate supported by an existing hard drive is the transmission rate 100 MB/s corresponding to mode 5. Signal phase shift between the controller and the hard drive may happen when the system is waken up to access the hard drive from a power saving mode of the system. Because the controller and the hard drive have to work in a synchronous access environment, when signal phase shift happens, the transmission rate of the hard drive and the controller have to be reduced (for example, from mode 5 to mode 4) to stabilize the system and write data into or read data from the hard drive. However, in the method described above, the maximum transmission rate (for example, the transmission rate 100 MB/s corresponding to mode 5) supported by the hard drive is sacrificed because of the requirement of the synchronous access environment. Namely, when the controller reads data from the hard drive, the hard drive should be able to operate at the transmission rate corresponding to mode 5 originally, but to avoid the problem of signal phase shift, the hard drive can only operate at the transmission rate corresponding to mode 4 lower than that corresponding to mode 5. As a result, the performance of the entire system is reduced.